Copper vs Steel boiler components

A special section just for steam engines and boilers, as without these you may as well fit a sail.
RGSP
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Re: Copper vs Steel boiler components

Post by RGSP » Sat Feb 11, 2017 9:32 am

cyberbadger wrote:Ron,

I just think they would probably laugh at me. I only need 1 tube.... :(

Fred - which would be a comparable specced copper tube?

-CB
Needing a single tube is not exactly unusual for a boiler tuber supplier however big a company they are: give them a call. You may have to buy an uncut length of maybe 20' or so, but that won't break the bank, and then you'll have some spare!

Willingale Tubes in England would certainly supply you with what you want, and are a very helpful bunch normally, but I suspect the shipping costs would be a bit prohibitive.
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Re: Copper vs Steel boiler components

Post by fredrosse » Sat Feb 11, 2017 12:05 pm

From RGSP:
"In truth, doing a precise quantitative measurement of heat input to a boiler isn't easy, and any differences were within experimental error. Amateur "enthusiasts" polarised into steel-loving and copper-loving camps, with scant regard for precise science.

From fredrosse on Steel vs Copper tubes:
"...heat transfer in the submerged tubes would go up from 62075 BTU per hour, to 62112 BTU per hour (18.193 kW to 18.204 kW), this is very very small increase."

In fact, the London Mechanics' Magazine article posted by cyberbadger which indicates far better boiler performance for copper tubes also has this statement: "The experiments of Mr. Tosh were subjected to a searching criticism by the engineers of the Institution, and strong doubts were expressed as to their correctness." These men knew the same technology and analysis methods used throughout the heat transfer community more than 100 years ago, and they knew the experimental results on this issue were meaningless.

In summary, unless you have test apparatus that can reliably recognize a difference in performance with four significant figures, and can maintain a test with applied conditions equally precise, then your test results would range from "highly unreliable" to "useless".
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Re: Copper vs Steel boiler components

Post by Ethelred » Sat Feb 11, 2017 12:47 pm

Does the different rates of expansion between copper and steel matter? As you can't weld the copper in aren't they more prone to leakage as a result?
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Re: Copper vs Steel boiler components

Post by DetroiTug » Sat Feb 11, 2017 3:24 pm

"I just think they would probably laugh at me. I only need 1 tube...."

Nahh, Wolverine tube is a very professional company. I dealt with a young lady, she worked up a quote and actually called me back when she said she would. (very unusual) I placed the order and they cut the flues, cleaned and chamfered the ends and even gave me one extra tube. I no longer have that available as it is the liner for my 103 caliber black powder rail gun. No steamboat is complete without one. :) I don't really think you're going to see anything conclusive by a slight change in one family of alloys. One has a range of products of high iron content, and the other predominantly of copper.

"unless you have test apparatus that can reliably recognize a difference in performance with four significant figures, and can maintain a test with applied conditions equally precise, then your test results would range from "highly unreliable" to "useless""

Which "four significant figures" are being referenced? I don't think the test I ran and they way it was ran was by any means perfect (is there such a thing?), but I don't think it was highly unreliable or useless. Everything was at same ambient temperature to begin, very close to the same amount of water in each. Same torch setting for both and the time was monitored very close. Perfect test? No, However, I do believe it showed that wall material type is not very important and there is no vast difference between steel and copper.

I could run a much better test, but I'm not going to invest the money in equipment needed, it simply isn't that important to me and would probably still only result in some similar outcome. It served to quell the suspicion I had.

As I eluded to above, many more qualified folks have obviously ran similar tests over the years with much better equipment and obviously arrived at a similar result as my rudimentary test. If there was a proven scientific opinion that copper was better than steel for heat transfer, it would not only be a good idea to use it, there would probably be Federal EPA mandates stipulating it's use where applicable.

-Ron
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Re: Copper vs Steel boiler components

Post by cyberbadger » Sat Feb 11, 2017 4:44 pm

I understand that the:

1) Difference is quite small
2) It is hard to measure without measuring a significant degree of error
3) Many have done this before.

These can be valid, but I get highly irritated when I wish to conduct my own tests and it is said it is not worth it because the results will be meaningless or a test is conducted and the results are written off as wrong because the steamboater doesn't have x number of decades in the industry.

That is not a constructive or helpful!

It is worth doing for the sake of science, the hobby, and other steam boaters. It is worth doing again because this is interesting and relevant to this hobby.

Suggestions to how improve a test, details, methodology, mathematics, physics that are relevant are what is needed, not blanket statements.

I'm still seeking the correct alloy and wall thickness for 1.25" diameter Copper firetubes that are ok for use in an ASME boiler.

-CB
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Re: Copper vs Steel boiler components

Post by Mike Rometer » Sat Feb 11, 2017 5:05 pm

Copper is NOT an alloy, it is a base metal (it may still be impure to some small percentage). If you alloy it, it will usually become Brass or Bronze. The possible variables in this experiment are immense. Identical wall thickness is only one. Even using propane as a heat source would be a variable, as the pressure from a new bottle will be different from a part used.

I by no means wish to decry any attempts as this is the way we all learn, but getting a "scientifically" acceptable result will not be easy.

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Re: Copper vs Steel boiler components

Post by cyberbadger » Sat Feb 11, 2017 7:18 pm

Mike Rometer wrote:Copper is NOT an alloy, it is a base metal (it may still be impure to some small percentage). If you alloy it, it will usually become Brass or Bronze.
There are plenty of Copper alloys that aren't Brass or Bronze.

McMaster-Carr has:
High-Strength 182 Copper
Easy-to-Machine 145 Copper
Super-Conductive 101 Copper
Multipurpose 110 Copper

Online metals also has:
C147 Free Machining Sulfur Copper
C122 Copper Tube is a commercially pure alloy of Copper. Like C101, C122 has no oxygen content; however C122 replaces the oxygen content with phosphorus.

-CB
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Re: Copper vs Steel boiler components

Post by Mike Rometer » Sat Feb 11, 2017 9:30 pm

For boiler work only copper (or steel) is allowed here. Bronze is allowed for bushings. Brass is a no. no, due to the possibility of de-zincification.
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Re: Copper vs Steel boiler components

Post by fredrosse » Sun Feb 12, 2017 5:47 am

“I get highly irritated when I wish to conduct my own tests and it is said it is not worth it because the results will be meaningless or a test is conducted and the results are written off as wrong because the steamboater doesn't have x number of decades in the industry.”

Sorry to have caused irritation, however I am just stating facts that are technically correct, using established engineering formulas which have been well known for more than a hundred years. I understand and commend the efforts to answer the Steel vs Copper issue with actual experiments, if they can be conducted with meaningful results. The mathematics here show that, to arrive at meaningful results, you will need instrumented apparatus capable of accurately identifying the difference between, for example, 18.193 kW and 18.204 kW. Instruments and experimental conditions with this level of precision are very difficult to attain, yet for the proposed objective of quantifying the benefits of Copper over Steel in the steam boiler heat transfer situation, this is the level of precision required.

The results of this type of testing are not “written off because the steamboater doesn’t have x number of decades in the industry”, they are constructively evaluated with real technical subject knowledge. Another relevant analogy that should be easily understood: if you want to machine a shaft for a press fit, and you have no micrometer, but only a wood yardstick, your machining efforts will be “highly unreliable” to “useless”. I think we can all understand this analogy, and the same holds true for the Copper vs Steel issue, but with more complex mathematics than a simple shaft measurement. Pointing this out to a person who might not recognize the error of using a wood yardstick to measure a shaft for a press fit is indeed “constructive and helpful!”.


Ron has stated it correctly with respect to his testing, “Perfect test? No, However, I do believe it showed that wall material type is not very important and there is no vast difference between steel and copper.” I think we all know and accept that Copper is a better heat conductor than Steel, yet Ron’s test shows the steel slightly better than Copper? Ron recognizes that his testing must be flawed in some way, (or that his measurement uncertianty is greater than the difference he is looking for) when his test shows Steel a better heat conductor than Copper, and the only conclusion he can draw from his test is that there is no important difference here.
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Re: Copper vs Steel boiler components

Post by RGSP » Sun Feb 12, 2017 8:57 am

Ethelred wrote:Does the different rates of expansion between copper and steel matter? As you can't weld the copper in aren't they more prone to leakage as a result?
That's a good question, because the expansion coefficients are indeed different by a significant factor, and in some circumstances it could cause problems. I think the best answer is to say that there have been thousands of boilers with steel drums and copper tubes over more than a century, and I've certainly never heard of tube joint leakage being a problem with them.

Of course, you do occasionally get weeping at tube--tubeplate joins, but such things are just as common in steel--steel joints. Think about this: especially during firing-up, ANY boiler has a whole range of temperatures for it's components, before they stabilise at roughly the same under working conditions. This is going to produce comparable stress to the expansion coefficient difference between steel and copper, and maybe more.

Incidentally, American terminology may be different, but in my book hard copper, soft copper, high conductivity copper etc. are not strictly alloys: they will have differing but small quantities of other elements present, but not enough to change the copper lattice structure - only distort it. If you add zinc or tin in large quantities then under microscopic analysis the whole metal structure changes, and you most often get different phases separating out in the grains as the alloy cools from molten.
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